A reported 20% of pregnant mothers in the United States in 1992 used nicotine and 5% used an illicit drug of some type during pregnancy. Just under half of the illicit drug use involved a psychostimulant (amphetamine or cocaine). Nicotine, amphetamine and cocaine exposure in utero have been associated with low infant birth weight, premature births, cognitive and other neurodevelopmental abnormalities. Yet drug use during pregnancy still occurs, presumably because of the many neurobiological and psychosocial factors that underlie drug abuse and dependence. The goal of the proposed research is to determine if hormone levels during and after pregnancy modulate the brain reward system and the reinforcing effects of a psychostimulant. In Aim 1, intracranial self-stimulation (ICSS) thresholds will be used to measure the sensitivity of the brain reward system in female rats administered a regimen of estradiol and progesterone that mimics pregnancy. ICSS thresholds also will be measured during withdrawal from the hormone regimen, to determine if the brain reward system is altered during the postpartum period. In Aim 2, ICSS and conditioned place preference procedures will also used to measure the reinforcing effects of d-amphetamine during the pregnancy regimen and the subsequent postpartum period.